Rainbows and Butterflies (and Volcanoes)

It’s a well-known fact in the sci-fi community that aliens often have weird-coloured blood. On Earth, however, blood is generally accepted to be red. We can further expand this notion to a variety of fluids, including tomato soup and lava. Or so it may seem from first glance. In reality, tomato soup in my kitchen generally adopts a sickly shade of green, and lava just occasionally happens to be blue. Only one of these statements should surprise you.

So, full disclosure. I’ve never actually made tomato soup, but that doesn’t stop the lava that seeps out of Indonesia’s Kawah Ijen volcano from looking blue. Before we get all excited, I need to admit that I’m twisting the truth a little. I’m making the broad (and in this case painfully incorrect) assumption that the hot fluid that leaks out of the fumaroles (vents) of Kawah Ijen is, in fact, lava. Rest assured, lava is red. Until it hardens into rock, that is. But the fluid we’re dealing with … is … actually also red. That is until the moment it bursts into flame.

The ethereal blue fire might look out of place, even magical in these photos, but to an experimental chemist the answer would be quite obvious. Sulfur. In fact, the fluid we’re dealing with is almost pure molten sulfur, which flows as a red liquid, burns with a blue flame, and hardens into a yellow solid. Because chemistry just makes that much sense.

We’re used to seeing this experiment play out with water, minus the fancy colors. At room temperature, water is a liquid. Cool it and it freezes into solid ice. Heat it and it boils to produce steam. What these photos show are similar processes with sulfur. Solid sulfur melts at a temperature of 115 C (239 F) to form a molten liquid. Sulfur doesn’t spontaneously ignite at the ambient conditions present in and around the volcanic vents – most of the blue flames are intentionally set by miners with flares. As it reacts with oxygen in the atmosphere, sulfur dioxide is produced – a sharp-smelling gas reminiscent of burnt matches.

This photo shows both the blue flame and the molten red sulfur underneath.

Stalactites (‘icicles’) of solid sulfur encrust an abandoned barrel.

These photos are taken within a cave system where miners break up the solid sulfur and haul it to the surface. Along their trek, they must make their way through a treacherous atmosphere of acrid gas, navigate the dark caverns with large sulfur blocks on their backs, scramble down the steep mountain slope, and deliver the mineral to be processed. All the while, they must take care to avoid the acidic lake that occupies the crater of the dozing volcano, which last erupted in 1817.

Be warned: you may have just sustained a lethal dose of mostly harmlessscience.

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I’m always torn when I’m dealing with a weird phenomenon that has an underlying explanation. In this particular case, I could probably dig into why the colours are so different, but it’s almost more exciting not to know 🙂